1. Field of the Invention
This invention relates to a method for the production of a catalyst useful in the polymerization of olefins and to a method for the production of highly crystalline olefin polymers.
2. Description of the Prior Art
It is well known that olefins can be polymerized using a Ziegler-Natta catalyst comprising a compound of a transition metal of Groups IV to VI of the periodic table and a metal of Groups I to III of the periodic table or an organo-compound of a metal of Groups I to III of the periodic table. Most commonly, the polymerization is performed at less than about 100.degree. C., and the polymers are obtained in a slurry form.
In this polymerization process, amorphous polymers are formed as by-products in addition to olefin polymers of high stereoregularity which are very valuable industrially.
The amorphous polymer has a low industrial value, and adversely affects the mechanical properties of products formed from the olefin polymers such as films and fibers. Moreover, the formation of the amorphous polymer consumes and thereby wastes the monomeric starting material, and an additional means is required to remove the amorphous polymer. This is a very serious industrial disadvantage.
It can be easily imagined therefore that substantial inhibition of the formation of amorphous polymers would be of great industrial advantage.
Furthermore, in this polymerization process, the catalyst remains as a residue in the resulting olefin polymers, and adversely affects the stability and processability of the polymers. Additional equipment is necessary, therefore, to remove the residual catalyst and stabilize the polymers.
These disadvantages of the process can be overcome by increasing the activity of the catalyst which is expressed as the yield of olefin polymer per unit weight of catalyst. If the catalytic activity is increased, no equipment for the removal of the residual catalyst is necessary and the manufacturing cost of the olefin polymer can be reduced.
In the production of olefin polymers such as propylene polymers and butene-1 polymers, titanium trichloride is most widely used as the transition metal compound which is a component of the solid catalyst.
The titanium trichloride used for this purpose is obtained by (1) reducing titanium tetrachloride with hydrogen and activating the reduction product by ball-milling, (2) reducing titanium tetrachloride with metallic aluminum, and activating the reduction product by ball-milling (the resulting compound has the general formula TICl.sub.3 (AlCl.sub.3).sub.1/3), or (3) reducing titanium tetrachloride with an organoaluminum compound at about -30.degree. C. to about 10.degree. C. and heating the resulting solid reduction product to about 120.degree. to about 180.degree. C. to change the crystal form of the solid reduction product.
However, the catalytic activity of the titanium trichloride thus-obtained is not entirely satisfactory and the stereoregularity of the polymers produced is also not entirely satisfactory. Thus, various improvements have been attempted.
As improved methods for the preparation of a titanium trichloride composition described above, Japanese Patent Publication Nos. 7074/1974, 48637/1974, 26376/1972, 1947/1974, 6828/1974 and 48638/1974 and Japanese Patent Application (OPI) Nos. 60182/1973 and 37176/1976 disclose methods for preparing the solid catalyst by ball-milling titanium trichloride together with other compounds and then washing the pulverized product with an inert solvent.
All of these improved methods require the pulverization of the titanium trichloride composition in a ball mill, and still the catalysts obtained have insufficient catalytic activity.
Further, Japanese Patent Publication No. 19155/1975 and Japenese Patent Application (OPI) No. 34281/1973 disclose methods for preparing the solid catalyst by washing titanium trichloride with organic ethers, organic thioethers or the like. However, the catalyst obtained has insufficient catalytic activity.
Still further, Japanese Patent Application (OPI) No. 34478/1972, for example, discloses a reduction product having a .beta.-type crystal structure, obtained by reducing titanium tetrachloride with an alkylaluminum and treating with a certain type of complexing agents, particularly, an ether compound, a thioether compound and a thioalcohol represented by the general formulas, R.sup.0 --O--R.sup.00, R.sup.0 --S--R.sup.00 and R.sup.0 --S--H, respectively and further with titanium tetrachloride. However, since the catalyst obtained using only a treatment with a complexing agent has catalytic activity as high as that of the above-described reduction product, the method as taught in the above-described Japanese Patent Application (OPI) No. 34478/1972 requires the titanium tetrachloride treatment in order to obtain a catalyst having sufficient properties.
Japanese Patent Application (OPI) No. 74595/1975 discloses that if the reduction product prepared by reducing titanium tetrachloride with an organoaluminum compound is treated with a complexing agent, then is treated with a monoalkyl aluminum dihalide to form a solid catalyst, and if such is subsequently treated further with a complexing agent, a catalyst for the polymerization of highly stereoregular active olefins can be produced.